The present invention relates to fabrication of semiconductor devices, and in particular, to a method and apparatus for polishing semiconductor wafers.
Chemical mechanical planarization (xe2x80x9cCMPxe2x80x9d) processes remove material from the surface of a semiconductor wafer in the production of ultra-high density integrated circuits. In a typical CMP process, a wafer is pressed against a polishing pad in the presence of a slurry under controlled chemical, pressure, velocity, and temperature conditions. The slurry solution generally contains small, abrasive particles that abrade the surface of the wafer, and chemicals that etch and/or oxidize the surface of the wafer. The polishing pad is generally a planar pad made from a relatively soft, porous material such as polyurethane. Thus, when the pad and/or the wafer moves with respect to the other, material is removed from the surface of the wafer by the abrasive particles (mechanical removal) and by the chemicals (chemical removal) in the slurry.
FIGS. 1 and 2 show a conventional polishing apparatus 10. The apparatus 10 includes a polishing pad 20 and three polishing stations 30, 40, 50 for polishing semiconductor wafers 60. Preferably, the polishing pad 20 spins counter-clockwise to accomplish the polishing of the wafers 60, as shown by directional arrow A in FIG. 2. Each station 30, 40, 50 includes a polishing arm 31, 41, 51 which holds the wafers 60 during the polishing process. Each polishing arm 31, 41, 51 includes a U-shaped member for holding vacuum chucks 32, 42, 52. Each polishing arm 31, 41, 51 includes one such vacuum chuck 32, 42, 52. The vacuum chucks 32, 42, 52 are coupled to U-shaped members through bearings 35, 45, 55. The bearings 35, 45, 55 allow the vacuum chucks 32, 42, 52 to rotate with respect to the respective polishing arms 31, 41, 51. The vacuum chucks 32, 42, 52 operate to hold the wafers 60 during the polishing process. Each of the vacuum chucks 32, 42, 52 includes an upper end 33, 43, 53 which may be coupled to a vacuum device (not shown) to provide a vacuum to the vacuum chucks. As can be clearly seen in FIG. 1, in the conventional polishing apparatus 10, the polishing stations 30, 40 each hold wafers 60, while the polishing station 50 is left empty (i.e. no wafer 60 is polished there). The polishing apparatus 10 also includes a slurry dispenser 70 which produces slurry which is dispensed onto a top surface 21 of the polishing pad 20.
A problem associated with the conventional apparatus 10 discussed above is that the slurry dispensed from slurry dispenser 70 often gathers in clumps on the top surface 21 of the polishing pad 20. Since the slurry is dispensed from the slurry dispenser 70 in droplet form, when the droplets hit the rotating polishing pad 20 they stay in droplet form and do not spread out. This clumping of the slurry results in uneven polishing of the wafers 60. In particular, when a droplet of slurry contacts a wafer 60, the initial area of the wafer that the slurry contacts is polished down further than the other areas of the wafer.
Therefore, there is currently a need for an improved polishing apparatus which provides an even distribution of slurry.
The present invention is an apparatus and method for polishing a workpiece including, a polishing pad; at least one polishing arm for holding a workpiece to be polished on the polishing pad; at least one conditioning arm for conditioning the polishing pad; and, a slurry-producing device, the slurry-producing device being disposed between the at least one polishing arm and the at least one conditioning arm so that slurry dispensed by the slurry-producing device contacts the at least one conditioning pad before it contacts the at least one polishing pad.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.